Post-Exposure Prophylaxis (PEP)

Reviewed by: HU Medical Review Board | Last reviewed: May 2024 | Last updated: May 2024

PEP (post-exposure prophylaxis) is a treatment option given after potential exposure to HIV has occurred. PEP involves taking a combination of antiretroviral medicines (ART).1-4

PrEP refers to medicines taken over a long time to prevent transmission of HIV. People who are at risk for being exposed to HIV may take PrEP every day. They take PrEP whether or not they have had a known exposure. PrEP helps protect the person taking it from contracting HIV.1,2

What is PEP?

PEP is a 28-day course of medicine. It is used in emergency situations after an exposure to HIV. Typically, the medicine must be started within 3 days after coming into contact with HIV.1

Why is PEP used?

PEP is an effective way to prevent HIV after a single, unexpected exposure. Taking PEP to prevent HIV may be advisable after situations such as:3

  • A condom breaking during sex with someone who may have HIV
  • Sharing drug injection equipment (needles, syringes, or cookers) with someone who may have HIV
  • Experiencing an accidental needle stick in a healthcare setting
  • Being sexually assaulted by someone who may have HIV

PEP is not intended for people who are already living with HIV or for long-term use by those at high risk for HIV. If you are in either of these situations, your doctor can prescribe an appropriate course of medicine for you. The best ways to prevent HIV transmission are to always:3

  • Use condoms if you have sex
  • Use clean needles if you inject drugs

How does PEP work for HIV prevention?

PEP is a type of short-term antiretroviral therapy (ART). These are drugs that prevent the virus from making copies of itself. In this way, ART reduces the amount of HIV in your body, known as your viral load. When the virus is suppressed with ART, your body’s immune system can better fight it and other viruses off.4

By providing your email address, you are agreeing to our Privacy Policy and Terms of Use.

To stop transmission in an emergency, PEP involves taking a combination of ART drugs at high doses. The specific drugs and doses may depend on your health needs. Children, pregnant people, and people with kidney disease may require unique drugs and doses.1,2

How is PEP given?

You must start taking PEP within 3 days (72 hours) after you were exposed to HIV. Research shows that it is not likely to be effective if started more than 72 hours after exposure. This is because HIV creates an infection in the body very quickly. The sooner you begin taking PEP, the more effective it will be.1,2

In certain cases of very high-risk exposure, a doctor may prescribe PEP up to a week after the exposure.5

Your doctor will tell you how to take your PEP drugs. Typically, you will take 2 drugs once or twice per day for 28 total days. Drugs involved in PEP treatment may include:2

  • Truvada® (combination of tenofovir disoproxil fumarate and emtricitabine)
  • Isentress® (raltegravir)
  • Tivicay® (dolutegravir)
  • Prezista® (darunavir)

Before prescribing PEP, your doctor may give you an HIV test, hepatitis test, pregnancy test, and other blood and urine tests. These tests help your doctor determine the right PEP drugs and doses for you.2

However, your doctor may tell you to begin taking PEP even before your test results come back so the medicine can start working. It is important to begin PEP quickly and take it exactly as prescribed.2

What are the possible side effects?

Like all drugs, PEP can cause side effects. Side effects can vary depending on the specific combination of drugs you are taking. They are usually mild and may include:2

  • Nausea or vomiting
  • Diarrhea
  • Fatigue

These are not all the possible side effects of PEP. Talk to your doctor about what to expect when taking PEP. You also should call your doctor if you have any changes that concern you when taking PEP.

If side effects of PEP are bothering you, your doctor may be able to adjust the combination or doses you are taking.

Paying for PEP

There are several ways to get help paying for PEP.

Your insurance may cover PEP, even if you are on Medicaid. If you do not have insurance or your provider does not cover PEP, your doctor can help you apply to have the cost covered by the drug company. You may also be able to apply for a discount yourself through the Medicine Assistance Tool.2

If you were exposed to HIV through sexual assault, the Office for Victims of Crime may reimburse you for your treatment costs.6

If you were exposed in your workplace, ask your employer whether their workers’ compensation or other insurance will cover your costs.6

Other things to know

PEP is not right for everyone. If you already have HIV or are taking PrEP, you should not take PEP. If you were exposed only to body fluids that do not transmit HIV, such as saliva, urine, or sweat, your doctor most likely will not prescribe PEP. If you are exposed to HIV often, your doctor may recommend that you begin PrEP after any necessary course of PEP.2

PEP is considered safe for adults and adolescents, as well as pregnant and breastfeeding people. In fact, it is especially important for pregnant people who think they may have been exposed to HIV to seek PEP treatment. This is because being pregnant increases your risk of contracting HIV through sex.2

While PEP is very effective, it is not 100 percent effective. You should continue prevention practices, such as wearing condoms, while you are on PEP. This will help prevent you from getting and transmitting HIV and other sexually transmitted infections while you are on PEP. Your doctor will test you for HIV again at regular intervals after you start taking PEP.3

If you have another exposure to HIV while taking PEP, you are likely protected by the original course of medicine. But your doctor may extend the PEP timeline past 28 days if you are exposed during the final 2 days of your original course. Some medical associations recommend extending PEP for another 2 to 28 days, depending on the type of exposure.7

PEP does not interfere with hormonal birth control or hormone therapy for transgender people. But PEP can interact with certain other drugs. Before beginning PEP treatment, tell your doctor about all your health conditions and any other drugs, vitamins, or supplements you take. This includes over-the-counter drugs.6,8